One of the central arguments made by In the Balance, Mark Tushnet's terrific new book about the current Supreme Court bench (reviewed here by Garrett Epps), concerns the counterweight to the conservative faction led by Chief Justice John Roberts. If Democratic nominees are able to wrest control of the Supreme Court back from the Republican nominees who have controlled the median vote on the Court for more than four decades, Tushnet argues, it is Elena Kagan who is likely to emerge as the intellectual leader of the Democratic nominees. And despite what many liberals feared, there is every reason to think that this would be an outcome supporters of progressive constitutional values would be very happy with.

When I say "many liberals," I include myself. My skepticism about the nomination, I should clarify, was not because I thought Kagan was a bad or unqualified nominee, or because I thought she was a closet reactionary. In the context in which Democrats had a more narrow majority, or had lost control of the Senate altogether, she would have been a solid pick. Given an unusually large Democratic majority, I thought it was important to get someone who was clearly a staunch liberal. While Kagan was not going to be a conservative I thought there was the possibility that she could be a moderate with some dubious views on civil liberties, a judge more in the mold of Stephen Breyer. Her history placed her broadly on the Democratic team, but her relatively thin academic writing record didn't produce many details about her views. She had never been a judge before her nomination.

Tushnet makes a good case that that these fears about Kagan were overblown. The most important evidence he cites? She didn't just clerk for the D.C. Circuit and the Supreme Court, impressive training grounds in their own right. She clerked for the liberal icons Abner Mivka and Thurgood Marshall. As Tushnet—himself a former Marshall clerk—points out, "Marshall left a great deal of drafting opinions to his law clerks, and Marshall and the committee of former clerks who screened their successors were careful to ensure that the clerks would be instinctively attuned to his views about the Constitution." Particularly in retrospect, it does seem like the Marshall clerkship is something that merited more weight when liberals were evaluation Kagan.

In addition, as Tushnet also points out, being part of the general Democratic or Republican constitutional "team" in itself provides much more information that it used to. As a result, the stakes of control of the Supreme Court are likely to be even higher in the future. In a fascinating recent paper, political scientist Mark Graber elaborates on this theme, describing the coming "constitutional yo-yo."

The key factors driving this change, Graber argues, are increasing polarization among elites and between parties. For example, the 40 years of Republican control of the Court I previously mentioned has often led to more modest and incremental change because the median vote has been controlled by moderate, country-club Republicans like Lewis Powell, Sandra Day O'Connor, and Anthony Kennedy—justices with generally conservative views who were liberal on some key issues such as privacy and gender equality. The decision rule on the court empowers moderates even if they're outflanked numerically on both sides.

The Court has frequently been in sync with national public opinion and moderates among political elites because party coalitions were so fractured. Both Woodrow Wilson and FDR appointed staunch liberals and southern segregationists to the Court, not because the latter were "mistakes" but because both factions were part of the Democratic coalition. Similarly, moderates and liberals like David Souter and Earl Warren were once a part of the Republican Party. But those days are done; it is overwhelmingly likely that Souter will be the last heterodox nominee for the foreseeable future.

(AP Photo/J. David Ake)

One upshot of this is that the Supreme Court is more likely to threaten major national policies than it was 20 years ago. The very narrow survival of the Affordable Care Act and the gutting of the Voting Rights Act reflects Supreme Court conservatives moving right along with the Republican Party. And that's with Kennedy's vote still being needed; the damage that a Court with Antonin Scalia or John Roberts as the median vote could be much more extensive.

Party polarization has not been symmetrical, and a Supreme Court with a Democratic median vote would be unlikely to have a similarly ambitious agenda.

If Kagan emerges as the voice of a Democratic majority, this would certainly be a positive development. In terms of votes, she's been extremely similar to the Court's current liberal anchor, Ruth Bader Ginsburg, voting with her 96 percent of the time. And not only has she had a very solid voting record, she has already made some substantial intellectual contributions. Like Tushnet, I'm particularly impressed by her brilliant dissent dissecting an illogical Roberts opinion striking down Arizona's public-financing law. And her academic work on presidential administrations is likely to be very valuable as the Court considers cases such as the D.C. Circuit decision all but reading the recess-appointment power out of the Constitution. Her record suggests she will be a powerful advocate for a federal government designed to work against Republican efforts to deliberately sabotage it.

The increasing predictability of Supreme Court justices has been good news in the case of Kagan. But there's a scary downside. Should the Republicans win the presidential election of 2016, substantial parts of the Great Society and New Deal are likely to be at risk. The increasing dysfunction of Congress is likely to be particularly in evidence if a nomination that will change the median vote of the Court comes before the Senate.